Phase synchronizing circuit

Abstract

A constant determination unit ( 90 ) determines various constants, that are the magnitude of a charge current outputted from a charge pump circuit ( 30 ), the time constant of a loop filter ( 40 ), and the gain of a voltage controlled oscillator ( 50 ), so as to make the proportionality constant of a natural frequency of a phase locked loop circuit for the input frequency of the phase locked loop circuit and the damping factor to be predetermined values, and outputs various control signals based on the determined constants. The charge pump circuit ( 30 ), the loop filter ( 40 ), and the voltage controlled oscillator ( 50 ) modify the magnitude of the charge current, the time constant, and the gain, respectively, in accordance with control signals outputted from the constant determination unit ( 90 ).

1. A phase locked loop circuit comprising:
 a phase comparator for phase comparison between a reference signal and a feedback signal; 
 a charge pump circuit for outputting a charge current based on a result of the phase comparison; 
 a loop filter for filtering the charge current; 
 a voltage controlled oscillator for oscillating according to an output voltage of the loop filter; and 
 an output signal frequency divider for dividing a frequency of an output signal of the voltage controlled oscillator and generating the feedback signal, wherein the charge pump circuit modifies a magnitude of the charge current in accordance with a first control signal, 
 the loop filter has a time constant modified in accordance with a second control signal, the voltage controlled oscillator has a gain modified in accordance with a third control signal, and 
 said phase locked loop circuit further comprising a frequency counter for measuring a frequency of an input signal, and a constant determination unit for determining constants, including the magnitude of the charge current, the time constant of the loop filter, and the gain of the voltage controlled oscillator, so that a proportionality constant of a natural frequency of the phase locked loop circuit for the frequency of the input signal and a damping factor have respective predetermined values, and outputting the first through third control signals based on the determined constants, 
 said phase locked loop circuit further comprising a first-order oscillator for oscillating according to a bias given to the charge pump circuit, 
 wherein the frequency counter counts, as the frequency of the input signal, a number of pulses of the input signal per cycle of the output signal of the first-order oscillator. 
 
     
     
       2. The phase locked loop circuit according to  claim 1 , wherein the first-order oscillator includes:
 a capacitor; 
 a first comparator for comparing magnitudes of a voltage of the capacitor and a first reference voltage, 
 a second comparator for comparing magnitudes of the voltage of the capacitor and a second reference voltage; 
 an RS flip flop receiving comparison results of the first and second comparators; and 
 a charge pump circuit for charging and discharging the capacitor with a current having a magnitude corresponding to the bias in accordance with an inverting output and a noninverting output of the RS flip flop. 
 
     
     
       3. A phase locked loop circuit comprising:
 a phase comparator for phase comparison between a reference signal and a feedback signal; 
 a charge pump circuit for outputting a charge current based on a result of the phase comparison; 
 a loop filter for filtering the charge current; 
 a voltage controlled oscillator for oscillating according to an output voltage of the loop filter; and 
 an output signal frequency divider for dividing a frequency of an output signal of the voltage controlled oscillator and generating the feedback signal, wherein the charge pump circuit modifies a magnitude of the charge current in accordance with a first control signal, 
 the loop filter has a time constant modified in accordance with a second control signal, the voltage controlled oscillator has a gain modified in accordance with a third control signal, and 
 the phase locked loop circuit further comprises a constant determination unit for determining constants, including the magnitude of the charge current, the time constant of the loop filter, and the gain of the voltage controlled oscillator, so that a proportionality constant of a natural frequency of the phase locked loop circuit for a frequency of an input signal and a damping factor have respective predetermined values, and outputting the first through third control signals based on the determined constants, 
 wherein the constant determination unit includes: 
 a gain selection unit for selecting any one of a plurality of values as the gain according to the frequency of the input signal; 
 a charge current determination unit for determining the magnitude of the charge current based on a first value, the first value being a product of a reference value of the charge current, a square of a ratio-to-reference of the input signal frequency, and a reciprocal of a ratio-to-reference of the selected gain; and 
 a time constant determination unit for determining the time constant based on a second value, the second value being a product of a reference value of the time constant and a reciprocal of the ratio-to-reference of the input signal frequency. 
 
     
     
       4. The phase locked loop circuit according to  claim 3 , wherein
 the output signal frequency divider has a modifiable frequency division ratio, and 
 the charge current determination unit determines the magnitude of the charge current based on a product of the first value and a ratio-to-reference of the frequency division ratio. 
 
     
     
       5. The phase locked loop circuit according to  claim 3 , further comprising an input signal frequency divider for dividing a frequency of the input signal and generating the reference signal, wherein
 the input signal frequency divider has a modifiable frequency division ratio, 
 the charge current determination unit determines the magnitude of the charge current based on a product of the first value and a square value of a reciprocal of a ratio-to-reference of the frequency division ratio, and 
 the time constant determination unit determines the time constant based on a product of the second value and the ratio-to-reference of the frequency division ratio. 
 
     
     
       6. The phase locked loop circuit according to  claim 3 , wherein
 the loop filter has a resistance value modified in accordance with the third control signal and has a capacitance value modified in accordance with a fourth control signal, 
 the constant determination unit includes a capacitance value selection unit for selecting any one of a plurality of values as the capacitance value of the loop filter according to the frequency of the input signal, determines the capacitance value of the loop filter, and outputs the fourth control signal based on the determined constants, 
 the charge current determination unit determines the magnitude of the charge current based on a product of the first value and a ratio-to-reference of the selected capacitance value, and 
 the time constant determination unit determines the resistance value of the loop filter based on a product of the second value and a reciprocal of the ratio-to-reference of the selected capacitance value. 
 
     
     
       7. The phase locked loop circuit according to  claim 3 , wherein
 the constant determination unit includes a proportionality constant selection unit for selecting any one of a plurality of values as the proportionality constant according to the frequency of the input signal, 
 the charge current determination unit determines the magnitude of the charge current based on a product of the first value and a reciprocal of a square value of a ratio-to-reference of 
 the selected proportionality constant, and the time constant determination unit determines the time constant based on a product of the second value and the ratio-to-reference of the selected proportionality constant.